Passport Ultra won't back-up

I initially had the Passport ultra set up to back up to the device and then accepted a complimentary upgrade to Pro. I decided i wanted to go back to the original setup i.e. to backup onto the device not the cloud. The only way to do that that i could figure out was to uninstall it and then reinstall it, but when i try to set up a ‘back-up plan’ i get the error message  "No writable partition.’

I’ve rerun the setup, and tried the Utilities for diagnostics, but nothing works.

Any suggestions?

Welcome to the WD Community.

Make sure that the portable drive is being detected by your computer. 

Also, make sure that you have your drive selected on the backup target area.